# Total differential

1. May 6, 2008

### hex.halo

1. The problem statement, all variables and given/known data

For:
z(x,y)=(x^2)y-3y
Find $$\Delta$$z and dz when x=4, y=3, $$\Delta$$x=-0.01, $$\Delta$$y=0.02

2. Relevant equations

3. The attempt at a solution

I got the partial derivatives:

df/dx=2xy, and df/dy=x^2-3

and solved dz=0.02

However, I don't know how to find $$\Delta$$z

2. May 6, 2008

### Dick

Delta z is the true difference. z(3.99,3.02)-z(4,3).